Conference Paper Study of Magnetic Property of Sn Doped Ni-Zn...
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Conference Paper Study of Magnetic Property of Sn Doped Ni-Zn-Fe Nanoparticles B. S. Tewari, Archana Dhyani, S. K. Joshi, Santosh Dubey, and Kailash Pandey Department of Physics, University of Petroleum and Energy Studies, Dehradun 248007, India Correspondence should be addressed to B. S. Tewari; [email protected] Received 5 February 2014; Accepted 11 March 2014; Published 9 April 2014 Academic Editors: R. Chandra, P. Mandal, R. K. Shivpuri, and G. N. Tiwari is Conference Paper is based on a presentation given by B. S. Tewari at “National Conference on Advances in Materials Science for Energy Applications” held from 9 January 2014 to 10 January 2014 in Dehradun, India. Copyright © 2014 B. S. Tewari et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e Ni 0.6+ Zn 0.4 Sn Fe 2−2 O 4 ( = 0.00 to 0.04) samples were prepared by solution route technique. ese samples were characterized by XRD and EPR spectra at X-band frequency (∼9.2 GHz). e XRD spectra of these ferrites confirm the formation of spinel structure. e average particle size calculated by using Scherrer’s formula was found to be of the order of 24.7 nm. e EPR spectra of these ferrites are mainly due to Fe 3+ ions. Fe 2+ ions have very short spin-lattice relaxation time and therefore EPR spectra of Fe 2+ could be observed only at very low temperature. is fact is also supported by the isomer shiſt values of these ferrites obtained from M¨ ossbauer spectroscopy. e variation of eff and Δ PP with Sn 4+ concentration is attributed to the variation of superexchange interaction. Moreover in this system the dominant process of relaxation is the spin lattice relaxation rather than the spin-spin interaction. 1. Introduction Ferrites are certain double oxides of iron and another metal taken as the most important ferromagnetic substances. e magnetic ferrites fall mainly into two groups with different crystal structures. One is cubic ferrites having the general formula MO⋅Fe 2 O 3 where M is a divalent metal ion, like Mn, Ni, Fe, Co, and Mg. Second one is hexagonal ferrites. e most important member in this group is barium-ferrites BaO⋅6Fe 2 O 3 . e ferrites are ionic compounds, and their magnetic properties are due to the magnetic ions they contain. e commercial value lies in the fact that they have higher values of saturation magnetization and Curie temperature, which are imperative for use as core materials. ey are more suitable for high power application in addition to the applications, such as multilayer chip inductor and elec- tromagnetic interference (EMI) suppression; recent studies suggest their applications in biomedical applications such as molecular imaging and drug delivery [1–4]. ere are two main classes of materials containing zinc ferrites, that is, Mn-Zn ferrites and Ni-Zn ferrites. Out of them Ni-Zn ferrites are designed for very high frequency operation, to more than 100 MHz as well as very high resistivity, about 10 5 ohm cm. e effect of TiO 2 addition on saturation magnetization and magnetic spectrum of Ni 0.3 Zn 0.7 Fe 2 O 4 has been studied [4]. An unexpected dip was reported in the saturation magnetization curve at a particular Ti 4+ concentration in Ti 4+ -substituted Ni-Zn ferrite [5]. It has also been concluded that lattice parameter decreased with the increase of Ti 4+ up to a certain concentration and subsequently it increased monotonically. e variation of lattice parameter with high valent substi- tution is a combined effect of cation size on [6]: (i) “”-the repulsion parameter for A site and (ii) “”-Madelung Constant. He also observed a similar type of anomalous behavior in saturation curve for a wide range of Ti-substituted Ni-Zn ferrites. e present work is done to record and analyse the electronic paramagnetic resonance (EPR) spectra of Sn-substituted Ni- Zn ferrite for various Sn concentrations at room temperature and liquid nitrogen temperature. e characterization of the prepared samples was done by XRD analysis. is work is a step towards studying the physical processes leading to anomalous behavior of magnetization in the Sn-substituted Ni-Zn ferrites [7, 8]. Hindawi Publishing Corporation Conference Papers in Science Volume 2014, Article ID 816970, 4 pages http://dx.doi.org/10.1155/2014/816970
Transcript of Conference Paper Study of Magnetic Property of Sn Doped Ni-Zn...
Conference PaperStudy of Magnetic Property of Sn Doped Ni-Zn-Fe Nanoparticles
B. S. Tewari, Archana Dhyani, S. K. Joshi, Santosh Dubey, and Kailash Pandey
Department of Physics, University of Petroleum and Energy Studies, Dehradun 248007, India
Correspondence should be addressed to B. S. Tewari; [email protected]
Received 5 February 2014; Accepted 11 March 2014; Published 9 April 2014
Academic Editors: R. Chandra, P. Mandal, R. K. Shivpuri, and G. N. Tiwari
This Conference Paper is based on a presentation given by B. S. Tewari at “National Conference on Advances in Materials Sciencefor Energy Applications” held from 9 January 2014 to 10 January 2014 in Dehradun, India.
Copyright © 2014 B. S. Tewari et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The Ni0.6+𝑥
Zn0.4Sn𝑥Fe2−2𝑥
O4(𝑥 = 0.00 to 0.04) samples were prepared by solution route technique. These samples were
characterized by XRD and EPR spectra at X-band frequency (∼9.2GHz). The XRD spectra of these ferrites confirm the formationof spinel structure.The average particle size calculated by using Scherrer’s formula was found to be of the order of 24.7 nm.The EPRspectra of these ferrites are mainly due to Fe3+ ions. Fe2+ ions have very short spin-lattice relaxation time and therefore EPR spectraof Fe2+ could be observed only at very low temperature. This fact is also supported by the isomer shift values of these ferritesobtained from Mossbauer spectroscopy. The variation of 𝑔eff and Δ𝐻PP with Sn4+ concentration is attributed to the variation ofsuperexchange interaction. Moreover in this system the dominant process of relaxation is the spin lattice relaxation rather than thespin-spin interaction.
1. Introduction
Ferrites are certain double oxides of iron and another metaltaken as the most important ferromagnetic substances. Themagnetic ferrites fall mainly into two groups with differentcrystal structures. One is cubic ferrites having the generalformula MO⋅Fe
2O3where M is a divalent metal ion, like
Mn, Ni, Fe, Co, and Mg. Second one is hexagonal ferrites.The most important member in this group is barium-ferritesBaO⋅6Fe
2O3. The ferrites are ionic compounds, and their
magnetic properties are due to the magnetic ions theycontain. The commercial value lies in the fact that theyhave higher values of saturation magnetization and Curietemperature, which are imperative for use as core materials.They aremore suitable for high power application in additionto the applications, such as multilayer chip inductor and elec-tromagnetic interference (EMI) suppression; recent studiessuggest their applications in biomedical applications such asmolecular imaging and drug delivery [1–4].
There are two main classes of materials containing zincferrites, that is, Mn-Zn ferrites and Ni-Zn ferrites. Out ofthem Ni-Zn ferrites are designed for very high frequencyoperation, to more than 100MHz as well as very high
resistivity, about 105 ohm cm. The effect of TiO2addition
on saturation magnetization and magnetic spectrum ofNi0.3Zn0.7Fe2O4has been studied [4]. An unexpected dip was
reported in the saturationmagnetization curve at a particularTi4+ concentration in Ti4+-substituted Ni-Zn ferrite [5]. Ithas also been concluded that lattice parameter decreasedwith the increase of Ti4+ up to a certain concentration andsubsequently it increased monotonically.
The variation of lattice parameter with high valent substi-tution is a combined effect of cation size on [6]:
(i) “𝑏”-the repulsion parameter for A site and(ii) “𝑀”-Madelung Constant. He also observed a similar
type of anomalous behavior in saturation curve for awide range of Ti-substituted Ni-Zn ferrites.
The present work is done to record and analyse the electronicparamagnetic resonance (EPR) spectra of Sn-substituted Ni-Zn ferrite for various Sn concentrations at room temperatureand liquid nitrogen temperature. The characterization of theprepared samples was done by XRD analysis. This work isa step towards studying the physical processes leading toanomalous behavior of magnetization in the Sn-substitutedNi-Zn ferrites [7, 8].
Hindawi Publishing CorporationConference Papers in ScienceVolume 2014, Article ID 816970, 4 pageshttp://dx.doi.org/10.1155/2014/816970
2 Conference Papers in Science
2. Experimental Technique
In the present work the EPR spectroscopy technique isemployed. EPR spectroscopy studies the interaction of elec-tron magnetic moment with a magnetic field and thus isapplicable only to the systems having unpaired electrons(paramagnetic substances) or net angular momentum. EPRspectrum can be used to identify an unknown transitionmetal ion or lattice defect; it may be used to distinguishbetween the several valence states of the same ion. EPRspectrum frequently identifies the lattice site and symmetryof the paramagnetic species, particularly if single crystaldata are available. Considerable information can be obtainedabout the nuclei in the immediate neighborhood of theabsorbing spin and sometimes relaxation time data detectslong range effects.The concentration of paramagnetic speciesmay also be determined.
The important parameters from the EPR signal to becalculated are
(i) 𝑔-factor . It is calculated as
𝑔 = 2.00367
𝐻DPPH𝐻𝑟
, (1)
where 𝐻𝑟in the original absorption curve is the field
corresponding to absorption (i.e., resonance field) for thegiven sample. In derivative curve it is measured.
(ii) Line width. It is defined as full width at half maximum(FWHM) for original absorption curve. For first derivativecurve it is given by the peak-to-peak distance along magneticfield axis; that is,
Δ𝐻pp = [𝐻 (peak 2) − 𝐻 (peak 1)] . (2)
(iii) Spin-spin relaxation. It is calculated using the for-mula 1/𝑇
2= 𝜋𝑔𝜇
𝐵Δ𝐻/ℎ, whereΔ𝐻 is the FWHM (full width
at halfmaximum)of the absorption peak or peak-to-peak linewidth of the first derivative curve.
3. Results
The EPR spectra of all the samples have an intense broadasymmetric peak having peak-to-peak line width Δ𝐻pp ∼ 2KGauss at room temperature. The spectra also have a veryweak shoulder near zero field. The appearance of this weakshoulder near zero may be due to anisotropy effect. Herewe are not interested in this particular investigation. Ourdiscussion will be confined only for the peak correspondingto 𝑔eff ∼ 4 for ferrites.
The graph plotted between 𝑔eff and the Sn concentration𝑥 at room temperature is shown in Figure 1. The 𝑔eff for baseferrite (i.e., 𝑥 = 0.00) is found to be 4.49 and it decreases to2.98 up to 𝑥 = 0.008. It again increases to 3.21 at 𝑥 = 0.012and then decreases to 2.95 up to 𝑥 = 0.04.
The variation of peak-to-peak line width Δ𝐻pp as afunction of “𝑥” in the Ni
0.6+𝑥Zn0.4Sn𝑥Fe2−2𝑥
O4(𝑥 = 0.00 to
0.04) ferrite system at room temperature is shown in Figure 2.The value of Δ𝐻pp for 𝑥 = 0.00 comes out to be 1.92 KGauss.
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045
7
6
5
4
3
2
1
0
gef
f
Sn concentration “x”
Figure 1: 𝑔eff versus Sn concentration “𝑥” inNi0.6+𝑥
Zn0.4Sn𝑥Fe2−2𝑥
O4at RT.
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045
2.5
2.0
1.5
1.0
0.5
0.0
ΔH
pp
Sn concentration “x”
Figure 2: Δ𝐻pp versus Sn concentration “𝑥” inNi0.6+𝑥
Zn0.4Sn𝑥Fe2−2𝑥
O4at RT.
It attains a maximum value of 2.225 KGauss at 𝑥 = 0.008and at 𝑥 = 0.012. It then decreases monotonically to a valueof 0.72 KGauss up to 𝑥 = 0.04. The variation of relaxationtime 𝑇
2with Sn concentration 𝑥 at room temperature is
plotted in Figure 3. For the base ferrite, Ni0.6Zn0.4Fe2O4, the
value of relaxation time comes out to be of the order of2.63 × 10
−11 seconds at room temperature. Here we do notobserve any systematic behaviour of relaxation time with Snconcentration. Previous workers [9–11] have also reportedsuch smaller values of relaxation time for Fe3+ ions.
The magnetic interaction causes broadening of theresonance lines as the temperature is increased, if theinteracting spins are alike, whereas it causes narrowingof resonance lines when unlike spins are involved. Sincein Ni
0.6+𝑥Zn0.4Sn𝑥Fe2−2𝑥
O4ferrite two different kinds of
paramagnetic spins, namely, Ni2+ and Fe3+, are involved, theexchange interaction might be responsible for narrowing ofthe resonance peaks with increase of temperature.
TheobservedEPR spectra of the ferrite studied here is dueto Fe3+ ions and not due to Fe2+ ions. The reason is that Fe2+
Conference Papers in Science 3
12
10
8
6
4
2
0
Rela
xatio
n tim
eT2
(×10−11) (
s)
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045
Sn concentration “x”
Figure 3: Relaxation time 𝑇2versus Sn concentration “𝑥” in
Ni0.6+𝑥
Zn0.4Sn𝑥Fe2−2𝑥
O4at RT.
ions have very short spin lattice relaxation time and EPR canbe observed at very low temperature (close to liquid Helium).Determination of isomer shift in this system of ferrite by 57FeMossbauer spectroscopy confirmed the fact that iron is inFe3+ state [12].
The value of 𝑔eff for bound unpaired electron is differentthan the value of 𝑔eff for a free electron. 𝑔eff for a boundelectron depends on the magnetic interaction involving theorbital angular momentum of the unpaired electrons. Sincethe chemical environment of the unpaired electron changesthe orbital angular momentum of the unpaired electron,therefore, one can say that 𝑔eff value likewise depends uponthe chemical environment of the paramagnetic ions underconsideration. The orbital angular momentum involves twotypes of magnetic interactions. One is the interaction of theorbital angular momentum with the electron spin, that is,the spin orbit coupling. The other interaction is that of theorbital angular momentum with the external magnetic field.The strength of these interactions affects the position and thewidth of the absorption peak in EPR spectra.
The occurrence of the finite line width in EPR spectrumis due to the fact that the electrons interact with externallyapplied magnetic field but they also interact magneticallywith the surrounding of the samples. Thus the resultantmagnetic field seen by a population of electron spins is notquite the same throughout the population evenwhen they aresubjected to the same applied field. Consequently resonanceabsorption line obtained for a given value of the resultant fieldwill be obtained over a range of values of the applied field.
In many magnetic materials the EPR study has revealedthat the variation of the resonance line width Δ𝐻pp is causedby the microscopic magnetic interactions inside the material,mainly the interparticle magnetic dipole interaction and thesuperexchange interaction. In the case of ferromagnetic par-ticles, the intrinsic molecular magnetic moments are large;therefore magnetic dipole interaction among these particlesis very strong. Magnitude of this interaction is inversely
proportional to the cube of average interparticle distance[13–15]. On other hand, superexchange interaction betweenmagnetic ions through oxygen anions can reduce the value ofΔ𝐻pp. The temperature dependence of relaxation time showsthat, if line width is determined by spin lattice relaxation,it will decrease rapidly as temperature decreases. Furtherthe elastic properties of these nanoparticles are currentlybeing studied for their specific applications of high frequencydevices [16].
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper.
References
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